Self-adhesive tapes which have high elastic or plastic extensibility and which can be redetached without residue or destruction by extensive stretching within the bond plane are known from, for example, U.S. Pat. No. 4,024,312 A, DE 33 31 016 C2, WO 92/11332 A1, WO 92/11333 A1, DE 42 22 849 C1, WO 95/06691 A1, DE 195 31 696 A1, DE 196 49 727 A1, DE 196 49 728 A1, DE 196 49 729 A1, DE 197 08 364 A1, DE 197 20 145 A1, DE 198 20 858 A1, WO 99/37729 A1 and DE 100 03 318 A1 and are also referred to below as strippable self-adhesive tapes.
These strippable self-adhesive tapes are oftentimes used in the form of adhesive film strips which are pressure-sensitive on one or both sides, preferably having a non-adhesive grip region from which the detachment operation is initiated. Particular applications of such self-adhesive tapes are found in publications including DE 42 33 872 C1, DE 195 11 288 C1, U.S. Pat. No. 5,507,464 B1, U.S. Pat. No. 5,672,402 B1 and WO 94/21157 A1. Specific embodiments are also described in DE 44 28 587 C1, DE 44 31 914 C1, WO 97/07172 A1, WO 98/03601 A1 and DE 196 49 636 A1, DE 197 23 177 A1, DE 197 23 198 A1, DE 197 56 084 C1, DE 197 56 816 A1, DE 198 42 864 A1, DE 198 42 865 A1, WO 99/31193 A1, WO 99/37729 A1, WO 99/63018 A1, WO 00/12644 A1 and DE 199 38 693 A1.
Preferred fields of use of aforementioned strippable adhesive-film strips include in particular the residuelessly and nondestructively redetachable fixing of light-weight and medium-weight articles in the residential, work, and office segments. For use in the work and office segments, the products used are generally of considerable thickness, of more than 400 μm.
In the consumer electronics industry—such as, for example, in the production of mobile telephones, digital cameras or laptops—there is an ever-growing desire for a possibility of separating the individual components on disposal after they have been used. Some components can then be reused or recycled. Or at least separate disposal is possible. There is therefore great interest within this industry in redetachable adhesive bonds. In particular, adhesive tapes which can be easily removed as and when desired, while possessing a high holding performance, constitute a reasonable alternative here to adhesive strips which must first be pretreated, by heating, for example, in order to be detached.
Within the consumer electronics segment, the preference is for adhesive strips which are extremely thin, since the end devices are extremely thin and hence all of the individual components are to take up little space as well.
When very thin strippable adhesive strips are used which operate without carriers, there is increased incidence of tears (see DE 33 31 016 C2). If the adhesive strips tear, then detachment is generally no longer possible, however, since the remnant of the adhesive strip springs back into the joint and there is therefore no grip tab available.
WO 92/11333 A1 describes a strippable adhesive tape which uses as its carrier a highly stretchable film with a resilience after stretching of <50%.
WO 92/11332 A1 describes an adhesive film strip which is redetachable by pulling in the bond plane and for which the carrier utilized may be a highly stretchable, substantially nonresilient film. Adhesives employed are exclusively UV-crosslinked acrylate copolymers, with which it is not possible to achieve the high bond strengths, and which undergo a smaller loss of peel adhesion during stretching than is the case, for example, for adhesives based on vinylaromatic block copolymer.
Further publications such as WO 2010/141248 A1 describe systems comprising pressure-sensitive polyisobutylene adhesives, which likewise exhibit a low peel adhesion.
A strippable adhesive film strip having a foamed, non-pressure-sensitive adhesive film carrier is described in WO 95/06691 A1, DE 196 49 727 A1, DE 196 49 728 A1, DE 196 49 729 A1 and DE 198 20 858 A1. Because of the intermediate carrier of foam material, a small thickness for the adhesive film strip, of below 200 μm, is not possible.
Foamed pressure-sensitive adhesive composition systems have long been known and are described in the prior art. In principle, polymer foams can be produced in two ways. One way is via the effect of a blowing gas, whether added as such or resulting from a chemical reaction, and a second way is via incorporation of hollow beads into the material matrix. Foams that have been produced by the latter route are referred to as syntactic foams.
Compositions foamed with hollow microbeads are notable for a defined cell structure with a homogeneous size distribution of the foam cells. With hollow microbeads, closed-cell foams without voids are obtained, the features of which include better sealing action against dust and liquid media compared to open-cell variants. Furthermore, chemically or physically foamed materials have a greater propensity to irreversible collapse under pressure and temperature, and frequently show lower cohesive strength.
Particularly advantageous properties can be achieved when the microbeads used for foaming are expandable microbeads (also referred to as “microballoons”). By virtue of their flexible, thermoplastic polymer shell, foams of this kind have higher adaptation capacity than those filled with non-expandable, non-polymeric hollow microbeads (for example hollow glass beads). They have better suitability for compensation for manufacturing tolerances, as is the rule, for example, in the case of injection-molded parts, and can also better compensate for thermal stresses because of their foam character.
Furthermore, it is possible to further influence the mechanical properties of the foam via the selection of the thermoplastic resin of the polymer shell. For example, even when the foam has a lower density than the matrix, it is possible to produce foams having higher cohesive strength than with the polymer matrix alone. For instance, typical foam properties such as adaptation capacity to rough surfaces can be combined with a high cohesive strength for self-adhesive foams.
EP 0 257 984 A1 discloses adhesive tapes which at least on one side have a foamed adhesive coating. Contained within this adhesive coating are polymer beads which in turn comprise a hydrocarbon liquid and which expand at elevated temperatures. The scaffold polymers of the self-adhesive compositions may consist of rubbers or polyacrylates. The microballoons here are added either before or after the polymerization. The microballoon-containing self-adhesive compositions are processed from solvent and shaped to form adhesive tapes. The step of foaming takes place logically after the coating operation. In this way, micro-rough surfaces are obtained. This results in properties such as, in particular, nondestructive redetachability and repositionability. The effect of the better repositionability by means of micro-rough surfaces of self-adhesive compositions foamed using microballoons is also described in other specifications such as DE 35 37 433 A1 or WO 95/31225 A1.
The micro-rough surface is used in order to produce bubble-free bonding. The same use is also disclosed by EP 0 693 097 A1 and WO 98/18878 A1. Self-adhesive compositions foamed using microballoons are also known from specifications U.S. Pat. No. 4,885,170 A and EP 1 102 809 B, where they are employed, however, as a filler for adhesive tapes for permanent bonding which are not redetachable.
Among the devices in the consumer electronics industry are electronic, optical and precision devices, in the context of this application especially those devices as classified in Class 9 of the International Classification of Goods and Services for the Registration of Marks (Nice classification); 10th edition (NCL(10-2013)), to the extent that these are electronic, optical or precision devices, and also clocks and time-measuring devices according to Class 14 (NCL(10-2013)), such as, in particular,                scientific, marine, measurement, photographic, film, optical, weighing, measuring, signaling, monitoring, rescuing, and instruction apparatus and instruments;        apparatus and instruments for conducting, switching, converting, storing, regulating and monitoring electricity;        image recording, processing, transmission, and reproduction devices, such as televisions and the like;        acoustic recording, processing, transmission, and reproduction devices, such as broadcasting devices and the like;        computers, calculating instruments and data-processing devices, mathematical devices and instruments, computer accessories, office instruments—for example, printers, faxes, copiers, typewriters—, data-storage devices;        telecommunications devices and multifunction devices with a telecommunications function, such as telephones and answering machines;        chemical and physical measuring devices, control devices, and instruments, such as battery chargers, multimeters, lamps, and tachometers;        nautical devices and instruments;        optical devices and instruments;        medical devices and instruments and those for sportspeople;        clocks and chronometers;        solar cell modules, such as electrochemical dye solar cells, organic solar cells, and thin-film cells;        fire-extinguishing equipment.        
Technical development is going increasingly in the direction of devices which are ever smaller and lighter in design, allowing them to be carried at all times by their owner, and usually being generally carried. This is now accomplished increasingly by realization of low weights and/or suitable size of such devices. Such devices are also referred to as mobile devices or portable devices for the purposes of this specification. In this development trend, precision and optical devices are increasingly being provided (also) with electronic components, thereby raising the possibilities for minimization. On account of the carrying of the mobile devices, they are subject to increased loads—in particular, to mechanical loads—as for instance by impact on edges, by being dropped, by contact with other hard objects in a bag, or else simply by the permanent motion involved in being carried per se. Mobile devices, however, are also subject to a greater extent to loads due to moisture exposure, temperature influences, and the like, than those “immobile” devices which are usually installed in interiors and which move little or not at all.